Redox Flashcards
What 2 steps should you do to the metal electrode before setting up the cell?
- Rid of surface impurities by cleaning with sandpaper
- Wash away grease (e.g. from hands) off the metal with propanone
What are salt bridges made out of?
Filter paper soaked in saturated KNO3
Where should the salt bridge be, and what is its purpose?
The salt bridge should be in both solutions, but not touching either electrode. The salt bridge completes the circuit, balancing the charges
What are electrochemical cells made up of?
Two half cells joined by a wire, voltmeter and salt bridge
What is the Ecell/EMF?
The potential difference between the two cells, as shown by the voltmeter
How do you set up half cells for two different ions of the same element (e.g. Fe2+ and Fe3+)?
Use a solution containing equal amounts of 1 mol dm-3 solution for each ion. In place of the metal electrode, use platinum
Why is platinum used as an electrode?
It is inert, but electrically conductive
How can you tell which half cell will be oxidised and which reduced?
NO PRoblem
The half cell with the most Negative electrode potential will be Oxidised.
The half cell with the most Positive electrode potential will be Reduced.
What happens to the half cell being oxidised?
The metal of this half cell will be dissociating more, so more electrons and ions are being produced, and some of these electrons will flow to the other half cell
What happens to the half cell being reduced?
There will be a net movement of electrons into this half cell
What observation will be seen about the metal being oxidised? (use Zn as the example)
The favoured reaction will be Zn(s) -> Zn2+(aq) +2e-
Therefore the metal Zn(s) will become thinner
What observation will be seen about the metal being reduced? (use Cu as the example)
The favoured reaction will be Cu2+(aq) + 2e- -> Cu(s)
Therefore the metal Cu(s) will become thicker
What would be the overall equation for a Zinc and Copper electrochemical cell?
Zn(s) + Cu2+(aq) -> Zn2+(aq) + Cu(s)
What is standard hydrogen electrode used for?
Standard hydrogen electrodes are used as a reference to measure standard electrode potentials
What is the E0 of the standard hydrogen electrode?
0V
What are the standard conditions for E0 values?
- 298K
- 100kPa
- Concentrations of ions at 1 mol dm-3
How do you get a 1 mol dm-3 H+ ion solution for the standard hydrogen electrode?
1 mol dm-3 of HCl or 0.5 mol dm-3 of H2SO4
How do you find the standard electrode potential of a half cell?
Connect the half cell to a standard hydrogen electrode under standard conditions
What are reducing agents?
Reducing agents lose electrons and are oxisised
What are oxidising agents?
Oxidising agents gain electrons and are reduced
How do you find E0cell?
E0cell = E0reduced - E0oxidised
Why do we use standard conditions for calculating electrode potentials?
Because the half cell is affected by changes in temperature, concentration and pressure
In cell notation, what do single vertical lines show?
A state phase boundary
In cell notation, what do two vertical lines show?
The salt bridge
